Radio object location system



May 24, 1949. w. H. DoHERTY RADIO OBJECT LOCATION SYSTEM 2 Sheets-Sheet 1 Filed Jan. 1, 1945 NVENTOR B? W H DO'ERTV A TTOR/VE V May 24, 1949- w. H. DOHERTY 2,471,264

RADIO OBJECT LOCATION SYSTEM elevation controls. and

Patented May 24, 1949 'y oFFlcE RADIO OBJECT LOCATION SYSTEM William H. Doherty, Morristown, N. J., assi'gnor' to Bell Telephone Laboratories, Incorporated,r New York, N. Y., a corporation of lNew York v Application January 1:1945, serial No. 570,939

i 4 Claims. (Cl. 343-11) This invention relates 'to improved arrangements for usein radars.

More specifically; it-

relates to improved ycombinations of exploratory y -wave scanning arrangements and data presentation arrangements for use in radars which 'expedite the processes of accurately finding and following azimuth and elevation angles and the yrange of specific lreflecting objects' or targets.

to a separate operator.

In order to avoid possible confusion between the selected target and one or more other objects at approximately the same azimuth and elevation angles, but at different range, it has further been c-ustomary to include in the range control system of the radar, aA range gate circuit which unblanks the train and elevation indicating circuits only during the instants at which reflected pulses are received from the selected target. In such systems, -the range operator must first align the range gate with the selected target before the other operators can start to bring the system into alignment in azimuth and elevation with the target so selected.

The above described arrangements are admirably well adapted for use with distant targets or even with slow moving targets at moderate range especially with systems having broad antenna eld patterns. However, for use at short range against hostile aircraft approaching at speeds in the order of hundreds of miles per hour, the delay of even a fraction of a second, necessitated'by the required setting of the range gate before the train and elevation operators can begin to align with the target, may prove disastrous.

A primary object of the invention is, therefore, to provide means whereby range, train, and elevation operators may all start immediately` to eiiect the alignment of the radar with any specific target without the necessity of waiting for the range operator toalign a range gate with the specific selected target.

A further difficulty is frequently encountered to assign each operationk with ship-borne or coastaldefense radars of the prior art in attempting to obtain the true elevation of aircraft ying relatively close tothe -surn face of the water in that the exploratory beamA has frequently been made relatively broad (or of wide angle) in the vertical plane, and hence, ln addition to the reectionsreceived directly from the aircraft, a second set of reflections returning from the aircraft 'afterreection from the surface of the Water arereceived, i. e., the radar in effect sees simultaneously-animage of the" aircraft in the water as well as the aircraft itself. I'hese two reflections one directly from the aircraft and the other from itsr image have a tendency to combine in the usual types of prior art radars and give an Yapparent elevation between the true elevation of the aircraft and the elevation of its image inthe water so that the elevation angle provided by the radar for fire control is apt tor be too small. The saine difliculty may also be encountered where land surfaces having highly reflective properties are present and the problem is that of Vdetecting low-flying aircraft.

A further object of the arrangements of the present invention is, therefore, to provide a type of radar system for use on naval vessels or at coastal defense installations whichv will give accurate and dependable elevation angle indications of` aircraft approaching at relativelylow elevation angles.'

In general, a-radar, to be effective for antiaircraft flre control purposes, must scan or otherwise cover an appreciable angle in both azimuthj .and elevation so that it will be readily possible to follow rapidly moving targets without losing them frequently. Convenient radar antenna scanning arrangements known in thelart permit rapid scanning to be effected in one plane only, so that scanning in the second plane must beat a relatively much slower rate. rAlso many antenna arrangements of convenient bulk and dimensions will provide an exploratory energy beam which is extremely sharp (or of small angular spread) in one plane but appreciably broader in the planel at right angles thereto. y

To meet particular demands, such as,for example, those of anti-aircraft radar service on naval vessels. therefore, the present invention vprescribes the use of rapid scanning in the vertical plane with an exploratory beam which is extremely sharp (or of narrow angle) in the vertical plane, so thatthe aircraft and its reflection or image in the water can be readily `and clearly distinguished from each other. A relatively much slower scan in azimuth will then not be seriously objectionable and can be entirely adequate for following all normal changes in the azimuth angle of an aircraft as it approaches. Since the desired accuracy in the azimuth angle indication can, as will presently appear, be readily obtained by use of a modification of the well-known method commonly designated as lobe-switching," a somewhat broader scanning beam in the azimuth plane will have advantages, in that reflections will be received from objects within the somewhat broader azimuth range thus afforded.

Furthermore, the systems of the invention include, in combination with the antenna system having the above described characteristics, means for portraying the radar indications of aircraft so that adjustments of the range, azimuth, and elevation controls of the radar to select a particular target can readily be effected simultaneously by the several operators normally employed, with no mutual interference. With systems of the invention, `a further advantage'is that a single type of indicator and electrical indicating circuit may be used by all three operators whereas prior systems at all comparable with those of this invention have required at least two different types of indicators and associated indicating circuits for the several operators.

The principles and additional objects of the invention will become more readily apparent during the course of the following detailed description of illustrative embodiments of the various features of the invention shown in the accompanying drawings in which:

Fig. 1 shows, in block schematic diagram form, 35 a simple arrangement of a radar system suitable for practicing the invention;

Fig. 2 illustrates the type of pattern provided by the indicator associated with the system of Fig. l;

Fig. 3 shows, in electrical schematic form, a range-sweep amplifler suitable for use with systems of the invention; and

Figs. 4 and 5 show voltage wave diagrams illustrative of the operation of the amplier of Fig. 3.

In more detail in the block schematic of Fig. l, oscillator l provides a simple sine wave having a frequency corresponding to the number of pulses it is desired to transmit each second.

The maximum permissible pulse rate is, of course, determined by the time interval required for a pulse to travel to an object at maximum range and to return by reflection to the radar system, added to whatever time interval may be required to restore the several apparatus units to the condition in which they will be prepared to repeat their` respective functions upon the emission of the next pulse. Usually, a much lower pulsing rate than the maximum permissible is employed, since the useful life of the active elee0 ments of the system can be substantially increased by reducing the pulsing rate.

For routine searching operations a pulsing rate as low as a few hundred pulses per second is sometimes employed, but for precise detecting 65 and ranging purposes, especially with respect to small rapidly moving objects, such as aircraft, pulsing rates between 800 to 4000 pulses per second are usually employed. Since systems of the present invention are primarily intended for de- 70 tecting and ranging in connection with aircraft at relatively short range, they will normally employ pulsing rates of a thousand or more per second.

Pulse generator I2 provides a pulse for each 75 4 cycle of the sine wave furnished by oscillator I0. Generator l2 can be of any of the several forms well-known to those skilled in the art and should preferably generate extremely short pulses of substantially square-topped contour. Modern radar systems employ square-topped pulses of from a small fractlonof a microsecond to several microseconds in length. Alternatively, the desired ccntroi pulses can be generated in any of the numerous other ways well-known to those skilled in the art as, for example, by use of a suitably proportioned multivibrator circuit.

The pulses from generator I2 are delayed a few microseconds, for example, 2 to 10 microseconds,

by delay unit Il which is adjustable and the purpose of which will be explained hereinafter. The pulses from unit Il are amplified in amplifier I4, the output of which energizes transmitter Il to emit similar ultra-high frequency radio pulses which energize the radiating elements 20 of the antenna system.

The antenna system can be, for example, of the general type described and illustrated in application Serial No. 453,390 of W. H. C. Higgins and C. A. Warren, filed August 3, 1942, which issued August 5, 1947 as Patent No. 2,424,982, which comprises a symmetrical linear array of dipole antennas placed end to end along-the focal line of a paraboloidal sheet reflecting member 22. Reflector 22 should be of sufficient depth and curvature to provide a directive beam which is sharp, or narrow, in the vertical direction.

Lobe switching in the horizontal plane of the dipole array is provided by -unit I8, the general arrangement being, for example, that illustrated in Fig. 11 of the above-mentioned application of Higgins and Warren and described in that application, though for the purposes of this invention a small number of dipoles on each side of the axis of symmetry can be employed. The lobe and scope switching mechanism I8 also includes a simple single circuit switch (scope switch) which is operated, by the shaft, the rotation of which effects the lobe switching action, to close while the mechanism defiects the antenna lobe in one direction and to open while the antenna lobe is deflected in the opposite direction. This switch can conveniently be, for example, of the commutator, wiper-spring type shown in Patent 2,143,035, issued January 10, 1939, to E. W. Smith (see items 18 to 22, inclusive, of the drawing of Smiths patent), or it can be a cam-operated switch of any of the numerous types well-known in the art. 'I'he purpose of this switch will become apparent in connection with the description of the amplifier of Fig. 3, hereinafter. In

general, the lobe position is switched or moved approximately the width of the lobe in the signal system.

The antenna system including reflector 22 is tilted vertically about pivot 2|, by crank 3| in the shaft 29 of motor 30 and connecting rod 33. to cause the antenna system to oscillate regularly through a small arc, for example, 16 degrees, in the vertical plane as motor 30 turns. The upper end of shaft 29 drives the lobe and scope switching mechanism I8 mentioned above, the entire mechanical linkage just described being proportioned so that the antenna system moves from its lowest to its highest tilt angle, while the lobe is switched in one direction, and from its highest to its lowest tilt angle, while the lobe is switched in the other direction. The purpose of the overall antenna scanning and lobe switching arrangements will also become apparent hereinafter. It

, the indicatorscreen to l ticular selected target in range. train which, as will presently appear, can be placed on opposite sides of the vertical center-line of facilitate following a par- (or azimuth) and elevation, simultaneously.

Echoes, or reflections, of the radiated ypulses 'from objects within the area scanned by the radiated energy are received by the antenna system and pass through the TR box I2, the converter 85, the intermediate frequency amplier 84 and the detector and video frequency amplifier 88 and are then applied to control element or anode 4II of cathode ray indicator 88 so that the intensity of the ray of the indicator will be increased each time a reflected pulse is received. The TR box is a resonant cavity tuned to the transmitted radio frequency and having shunted across a major potential gradient thereof a gas tube which breaks down when subjected to the high energy transmitted pulses, thus detuning the cavity and protecting the receiving circuits from damage o'r blocking by overloading. At the end of each transmitted pulse the gas tube recovers substantially instantaneously so that reilected pulses will freely enter the receiving apparatus.

The lower end oi' shaft 28 of motor 30 drives insulating arm 25 carrying' contactors 21 of circular potentiometer 28, across the winding of which is connected a potential source or battery 28, as shown. The variable voltage ofthe potentiometer is connected across the vertical deflectfound to befconvenient to proportion `the relativedelays through the yseveral portions of the system so. that the range mark' will normally occur at the center point ofthe sweep with unit 50 set to zero delay and also so that a reected echo from an object at substantially zero range will occur at the same point as the range mark when adjustable delay units 54 and 50 are both set to zero delay.

' uming, as above suggested, a precision sweep of 10 microseconds, it is obvious that the 'range mark should, preferably occur 5 microsecondsafter the start of the precision sweep. As above mentioned, the pulse controlling the precsion sweep originates in pulse generator I2 and passes through units 54. 50. and the range sweep generator 48, before reaching range sweep amplier 48. Also, the pulse controlling thev range vmark originates in pulse generator I2 and passes through units 54 and 5I before reaching range mark generator 52. From this it is apparent that adjustable delay unit 5I shouldbe adjusted so that its own delay and that vof the range mark generator 52 should exceed the delay of units A50, 48, and amplifier .48, by precisely 5 microseconds. I

Furthermore. it is apparent that, in order that a reflected p'ulse from an object at substantially zero range arriveat oscilloscope 88 at the same instant as the range mark, the total delay of a pulse in passing through units II, I'4, I8 and I8 to antenna 20 and by reflection back through umts 20, I8, 32, 35, 84, and 38, must just equal the delay of a pulse passing through the aboveing plates 44 of oscilloscope 88, as shown in Fig.

1, and serves to deflect the ray of the oscilloscope vertically in synchronism with the vertical tilting motion of the antenna system (i. e., the ray sweeps from its extreme lower position to its extreme upper position as the antenna is tilted through its corresponding range of motion, etc.)

The entire antenna system, with associated controls I5, is provided with means for turning it in azimuth and in elevation. This means can be, for example, similar to that shown in Fig. 5 of United States Patent 2,231,929', issued February 18, 1941, to J. Lyman, employed for like purposes. In Fig. 1 of the accompanying drawings, scales 8l and 58 are associated with controlsli and 82, respectively, as shown, from index marks 88 and 85, of which the elevation andA azimuth angles of system I5 can be read directly.

Range sweep 'generator 48 preferably provides conventional linear saw-tooth voltage lsweep waves of either of two lengths, the longer one to cover the full useful range of the radar system and the shorter oneto provide an expanded or precision range over a portion, for example, a l-microsecond interval, ofy the full range. The range sweep is amplified in a special form of sweep amplifier 48, described in detail hereinafter, and then applied/to the horizontal deflectiflg plates 42 of oscilloscope 38.

The range sweep desired is selected by moving sweep selector switch 14 to its main or precision" position. The full or main sweep is synchronzed -with the outgoing radar pulses by energy pulses derived from pulse generator I2 through unit II over circuit I3 and the precision range sweep is synchronized by energy pulses over circuit 13, which, though also derived from generator I2, pass through adjustable delay units 54 and 50 before reaching swep generator 48.

When using the precision sweep, it has been traced circuit, including units 54, 5I, and 52.

Delay unit II is, therefore, adjusted to establish the desired condition. A

Unit providesconvenlent means, when using thelO-microsecond precision sweep, for bringing the left'and right range lines, after alignment with the selected target, into closer proximity to facilitate the comparison of the amplitudes of left and right lobe reflections from the selected target, as will be described in connection with Fig. 2. 1

The arrangement of umts 48, 50, 5I, 52, and 54, as above described in detail, provides a convenient arrangement, in that the expanded section of the sweep can be definitely related to the range at which adjustable unit 54 is set, since with unit 50 adjusted to zero delay, the range marks from generator 52 are adjusted'to occur in the center of the precision sweep for any setting of unit 5 4.

YThe selected range sweep is, as `mentioned above, ampliiied in amplier 48. The output circuit of this amplifier is balanced and is adjusted so that the cathode ray of oscilloscope 38 will start from the vertical double center line 228 (Fig. 2) inscribed on .the oscilloscope screen.

The two lines of double line 230 are closely spaced. A single line could obviously be employed to indicate the center of the screen, but use of the double line, as shown, avoids possible confusion (or overlapping) of the right and left indicator patterns, as will be more readily understood in connection with the description hereinunder of a.

suitable form ,of the sweep amplifier 48, shown in Fig. 3. The beam of the oscilloscope will be de- :7 switch, a suitable voltage source being, of course, included in the circuit to operate the relay when required. A preferred form of the amplifier 40' is, as above-mentioned, shown in Fig. 3 in electrical schematic diagram form and will be described in detail hereinafter. l

Pulses from generator i2 are also impressed upon range mark generator 52 after passing through adjustable delay units 5I and 54. Unit 54 is provided with an adjusting knob and pointer 53 and a scale 55 calibrated in yards or other convenient units of range. Unit Il, as stated above, provides for the initial adjustment of the zero" position of the range marks to coincide with the center point of the precision sweep when unit 50 is set at zero. The range marks from unit 52 are applied to the control anode 40 of oscilloscope 38 and provide right and left range marks whichV take the form of vertical lines and can be aligned with the right and left reflections or echoes from a target of particular interest by adjustment of unit 54.

Range adjustments are usually made with reference to the leading or front edge of the reected pulse, for example, the edge nearer the center lines 230 of oscilloscope screen 200, as shown in Fig. 2, since this is normally a welldefined point and the process, therefore, facilitates adjustment. When so adjusted, the range of the object from which the selected reilection is received can be read directly from the scale 55.

Adjustment of unit 50 when using the precision sweep can, as mentioned above, be employed to bring both the left and right range marks and the target indications aligned therewith nearer to the vertical center lines 230 of the oscilloscope screen 204 of Fig. 2, and thus facilitate the comparison of the amplitudes of the left and right lobe indications of a given target to determine the precise adjustment of az'muth control 62 required to align the axis of the antenna in azimuth with the target. The azimuth of the target can be read on scale 63 when the right and left indications from aselected object are of equal amplitude.

A preferred type of indication provided by systems of the invention, such as that illustrated in Fig. 1, is illustrated in detail in Fig. 2, where double line 230, as mentioned above, represents the vertical center of the oscilloscope screen 200 and elevation line 240 is the horizontal center line thereof. Elevation line 240 corresponds, as mentioned above, to the mid-position of the tilting movement imparted to the antenna reector 22 by the crank and rod mechanism 3|, 33 of Fig. 1. The elevation of a selected target can -be read from scale 6| when control G0 has been adjusted so that line 240 bisects the reflected indication received therefrom.

Indications obtained with the antenna lobe in its left position are shown to the left of double line 230. Those with the lobe in its right position are shown to the right of double line 230. It is assumed, for purposes of explanation, that the system is being used on `a marine surface craft and that two low-flying aircraft are within the area in range, elevation and azimuth at the moment covered by the radar system.

For the left lobe pattern, these two aircraft are represented by indications 2I0 and 2|0, respectively. -Indications 2l2 and 220 are the reflections in the water of these two aircraft, for

sponds, as mentioned above, to the midposition T The elevation angles of these targets with respect to the elevation line 240 (orthe center of the tilt range) are indicated by their respective vertical positions on the screen, object 2i! being centered with respect to the elevation line 240 and object 210 being about 6 degrees above the elevation line, assuming, as indicated, a total tilt of 16 degrees, namely, 8 degrees above and 8 degrees below the elevation line. The lrelative ranges of the objects 210 and 2 I0 are represented by their respective relative horizontal displacements to the left from the vertical center line 230 for the left half of the indicator pattern. The range is, of course, accurately determined for any selected reflection by adjusting unit 54 to bring the vertical range line 202 into coincidence with the leading edge of the selected reflection and reading scale 55, as previously described.

0n the right half of the indicator screen a substantially identical pair of indications 2H and 20B, with their reections in the water 2|6 and 208, respectively, are obtained, except that their respective relative ranges are indicated by displacement to the right of center line 230 and their relative amplitudes with respect to corresponding indications on the left half of the pattern will differ if the amplitude of reflections received when using the right antenna lobe are different from the amplitude of reflections received when using the left lobe.

In the illustrative over-all pattern of Fig. 2, the "right lobe indication 2M is shown as being of substantially identical amplitude with the corresponding left lobe indication 2|8, indicating that the antenna system has been adjusted properly in azimuth to give the true azimuth bearing of the object from which these reflections arebeing received. Indications 2M and 218 are furthermore centered vertically with respect to the elevation line 240, indicating that the antenna system has been adjusted properly in elevation to the true elevation angle of the object from which these reflections are being received. Accordingly, the azimuth and elevation angles 0f this particular object can be read from scales 63 and 6I, respectively, of Fig. 1, as described above. I

The range marks which form the dotted lines 202 have been adjusted by unit 5l to coincide with the leading or nearer edges of indications 2M and 2I8 and hence the range of the object may be read directly from the calibrated range scale 55 on unit 54.

It should be noted that, when using the precision sweep, all indications, including both of the indications 2H, 2I8, and the range lines 202, can be brought closer to the Vertical center line 230 by adjustment of unit 50, the operator bringing them sufiiciently close together so that it can be easily judged when they are of identical brightness and size. This adjustment does not affect the actual range of the object but merely shifts the entire range scale on each half of the indicator pattern to facilitate the matching of a particular chosen pair of left and right lobe indications as described.

Considering the right lobe indication 206, its amplitude is apparently greater than that of its corresponding left lobe indication 210 as evidenced by its greater brightness (the degree of brightness is indicated by the Weight of the lines) and somewhat larger size. This indicates, of course, that the antenna system should be turned to the left if it is desired to determine the precise azimuth of theMobjectU-froxn 'which indicavious `thatthe elevation of the yantenna system should -be increased until the elevation line 240 bisects indications 206, 2 I 0 ii' the precise elevation of the object is to be obtained. Likewise, to facilitate amplitude comparison, unit 50 should be adjusted to bring the two indications 206, and 2l0 into closer proximity and unit 54A should be adjusted to bring the lines of range marks 202 into coincidence with the leading edges oi indications 206, 2I0 to obtain the range. When the above indicated adjustments have been made, indications 206. 2I0 will have been brought into substantially the positions occupied in Fig. 2 by indications 2I4, 2I3 and the azimuth, elevation, and range of the second object may then be read from scales 63, 6I, and 55, of Fig. 1, respectively.

An alternative type oi'. ,indication which could be employed with systems oi' the invention, is that in which the-left lobe pattern of indications is superimped upon the right vlobe pattern of indications but displaced by a small arbitrary interval to the right. To providesuch an indication the direction of the range sweep would be the same i'or each pattern but the starting line for the two patterns would, of course, be displaced by the aforementioned slight interval. With such a composite indication, each right lobe target indication would have the corresponding left lobe target indication beside it and it would not be necessary to manipulate an apparatus unit to bring them close together i'or the purpose oi am'- plitude comparison. Such an arrangement would, however, in some cases, involve a sacriilce of the ease with which corresponding left and right lobe indications oi a particular target could be identied. The general method is, of course, an extension of that of matching left and right lobe indications from a single target, other indications being excluded by gating the receiver. This latter method, employed in numerous prior art object detecting systems, is described for example in the above-mentioned application of Higgins and Warren.

It is apparent from the above description that where the three alignment processes necessary, i. e.,.alignment in azimuth, elevation and range, have been assigned to three'separate operators,

f respectively, all three operators may cooperate and manipulate the several controls simultaneously to bring a particular pair of indications into the desired alignment. Obviously, this cooperative effort can, furthermore, be continuously applied in order to follow the movement of a rapidly moving target such as an aircraft.

Data transmitting systems can also readily be devised by those skilled in the art to be mechanically connected to the shafts of the three adjustment controls to forward train (or azimuth), elevation and range data to a gun director or fire control station. Such arrangements are well known in the art, one form being described. for example, inthe above-mentioned patent to Lyman. Also. antiaircraft guns can be arranged to follow the movements of the antenna, with appropriate corrections by auxiliary controls for target speed, range and windage, and the firing oi' the guns can be controlled by an officer who has before him a duplicating indicator showing when the radar is being maintained precisely in l alignment with the target.

Also, separate duplicate Oscilloscopes can be 0 provided for each radar operator so that they may more conveniently perform their several i0 functions. Moreover, aided drives' to facilitate the tracking oi rapidly moving targets or fully automatic tracking arrangements, well known in the art, can be provided and given partial or i'ull control of the radar system and associated 81m directors, oncea deiinite target has been selected and the radar system-aligned thereon.

In Fig. 3, a suitable type of range sweep amplifier, for use as ampliiler 46 in the system of Fig. 1, is shown in schematic diagram form. This ampliiler is described in detail in the copending application of E. 'A. Krauth, Serial N0. 568,989, led December 20, 1944, assigned to applicants assignee, and the novel features thereof are claimed in the Krauth application. i

A saw-tooth sweep wave voltage, such as' that indicated by wave 360 for the main or full range sweep. or by a "shorter" wave 310 for the precision sweep, is impressed upon terminal 302 by range sweep generator 48 of Fig. 1, according to the position of sweep selector switch 14. v

The precision sweep diilers from the main sweep only in having a Steeper slope andconsequently shortery duration which, of course, means that the ray oi.' the oscilloscope will traverse the screen more rapidly and thus, in eii'ect. expand a portion of the main sweep to provide increased precision in range observations within the expanded portion.

In Fig. 3, a double-pole, double-throw switch 306 is mechanic-ally coupled to an electromagnetic device 3I2, such, for example, as a solenoid, having an armature 3I I, which is operated by energy from a battery 3I6, when terminals 332 are short-l circuited by the closing of the single circuit switch mentioned above (inthe lobe and scope switching mechanism I8 of Fig. 1). to which they are f leased and spring 308 contracts, throwing switch 306 to its upper or left" position.

'I'he ampliiler of Fig. 3 is of the phase-inverter, cathode coupled type..known to those skilled in the art, which provides a balanced output but operates from an unbalanced input. The positive terminals of 3D0-volt direct current potential sources, not shown, but which can be simple bat- Ateries or suitable rectiilers operating from alternating current supplies, are connected to terminals 3|8, 320 and 324, as indicated and theA positive terminal of a 45o-volt direct current source, not shown, is connected to terminal 322, as indicated, of the ampliiier, for normal operation, the negative terminals of all said sources being grounded. Alternatively, a unitary potential source providingl +300 volts and +450 volts direct current, its negative terminal being grounded, can be employed and suitable isolating impedances employed in the several circuits just mentioned, in accordance with principles well known to those skilled in the art. f

With switch 306 in its upper position, potentiometer 304 provides a convenient means for adjusting the potential of the control gridl (the grid immediately adjacent the cathode) of pentode, vacuum tube 333. Similarly, with switch 306 in its lower position, potentiometerld provides means for adjusting the potential of the control grid of p entode vacuum tube 342. The

second or middle grids of both oi these pentodes are connected together and through resistor 334 to the positive 30D-volt supply normally connected to terminal 324. The third grids (immediately adjacent the anodes) oi both pentodes are connected to vtheir respective cathodes, which latter are connected together and through resistor 336 to ground. The anodes of pentodes 338 'and'342 connect directly to output terminals 323 and 330, respectively, and through load resistors 346 and 350, respectively, toterminal 322 which is normally maintained at 450 volts (positive) with respect to ground. A voltage divider com' prising resistors 352 and 354 maintains terminal 323 at a potential midway between the potentials at terminals 326 and 330.

In the usual terms employed in the art, with switch 306 in its upper or left position, the circuit including vacuum tube 342 is a single stage amplier and the circuit including vacuum tube 338 'is a phase inverter stage coupled to the amplifier stage through the cathode resistor 333, common to .these two circuits. This arrangement provides a control grid (i. e., the grid nearest the cathode).

This biasing circuit comprises potentiometer 304, the ungrounded terminal 320 of which is connected to the positive terminal of a 3D0-volt direct current source, as previously mentioned.

This use of an adjustable independent bias facilitates the adjustment of the balance of the amplier and further contributes towards the ease with which a reversal of the polarity or direction of the amplified sweep wave appearing across terminals 326 and 330 can be effected, since by simply operating the solenoid 3| 2 (by the short-circuiting of the terminals 332 as described above) to throw switch 306 to its lower (or right) position it is at once evident that the circuit including vacuum tube 338 now becomes the amplifier vstage and the circuit including vacuum tube 342 becomes the phase inverter stage. The control grid of this latter stage now derives its bias from potentiometer 3|4 the ungrounded terminal 3| 8 of which is connectedvto the positive terminal of a 300-volt direct current supply source, as men- -tioned above. The desired reversal of polarity at terminals 326, 330 is thereby accomplished.

The use of a double vertical center line between the two images on the screen of an associated oscilloscope, or equivalent indicating device, such as the double line 230 of Fig. 2, in combination with the exibility of adjustment ail'orded by the provision of an independent adjustable bias on the control grid of either tube 333 or 342, when acting as the phase inverter, facilitates adjustment of the horizontal left and right sweeps to zero since each can then be made to coincide with the nearer one of the lines 230. If a single line were employed it would be somewhat more dimcult to determine when both the right and left horizontal sweep lines had been adjusted to prelcisely coincide with their respective zero lines without overlapping the other image. Also deviation from the zero lines during normal opera- Y 12 tion of the system is more readily detected if two separated zero lines are employed.

In passing it should be noted that the insertion ofa polarity reversing switch at terminals 323, 330 is not practicable, nor desirable, because of the high potentials and high impedance levels involved at this point in the circuit..

The operation of the reversible balanced sweep ampliiler of Fig.` 3 isillustrated by the voltage waves shown in Figs. 4 and 5.

Fig. 4 illustrates the approximate-voltage relations existing at the control grids, plates (anodes) and in the grid-cathodes circuits (En) of the pentodes 333 and 342 of the amplifier of Fig. 3 when switch 303 is. in the lower or right (R) position. The straight horizontal lines at the left of Fig. 4 show these voltage relations when no sweep impulses are being furnished to terminal 302 of Fig. `3.

Lines 400 and 40| represent the potentials of the anodes of tubes 342 and 333, respectively. Lines 4I0 and 4I2 represent the potentials of the control grids of tubes 342 and 333, respectively. Lines 420 and 422 represent the Potentials developed in the grid cathode circuits of tubes 342 and 338, respectively.

When the sweep is on and sweep pulses, such as 360 or 310, are being furnished to terminal 302, Fig. 3, the voltage relations shown at 'the right of Fig. 4 obtain. l

The anode of tube 342 has its interpulse value of +300 volts, line 400, and rises linearly to a maximum approaching +450 volts, line 402, returning more `rapid1y,.line 403, to +300 volts, while the anode of tube 333 has an interpulse value of +296 volts, line 40| which decreases linearly to a minimum approaching volts, line 404, returning more rapidly, line 408, to +296 volts s'o that the average potential of the anodes of tubes 342 and 338 remains constantly +298 volts. This is, of course, the recognized optimum condition for maintaining a good focus of the beam of the associated cathode ray oscilloscope, throughout the entire sweep of the ray in response to the deflecting voltages.

'Ihe grid voltage variation of tube 333 is represented by lines 4|2, 414 and 4|6 for the abovedescribed variation cycle, the grid of tube 342 remaining constant, line 410.

The grid-cathode circuit voltage cycles for tubes 342 and 348 are represented by lines 420, 428 andv 430 and lines 422424, and 423, respectively, for the above-described variation cycle of anode potentials. l

In Fig. 5 the voltages and their variation cycles are .represented for the upper (or left) position of the switch 306. From inspection it is obvious that they are identical but interchanged with respect to the two tubes 342 and 333 so that the output voltages appearing between terminals 326 and 328 and between 330 and 323 are merely interchanged. In other words, for the no sweep condition illustrated at the left in Fig. 5, the anode potential of tube 338 is now +300 volts, line 5H, while that of the anode of tubel .342 is +296 volts, line M3. Thecontrol grid voltage of tube 342 is +30.0 volts, line SI2, and that of tube 333 is +298 volts, line 5I4. The grid-cathode circuit voltage of tube 342 is 1.8 volts, line 5|3, and that of tube 333 is -2.0 volts, line 520.

For the "sweep on condition illustrated to the right of Fig. 5, the anode voltage of tube 333 follows lines 500, 304 and 306 and that of tube 342 follows lines 502,' 303 and 5I0. The control grid that of tube 338 is constant +29.8 volts, line Bil.`

The grid-cathode circuit voltage of tube 342 Iollows lines lll, 522 and 524 while that of tube 338 follows .lines 520. 528 and 532, as shown lin Fig. 5. It is thus apparent that a right or-left deilection of the ray of the oscilloscope from a, position near the center of the screen can be obtained by the arrangement of Fig. 3, the direction of sweep being determined by the position ot switch 308. It

1 should be noted as a desirable condition that the average of the anode (or plate) `voltages of the two vacuum tubes should be substantially the same for both leit and right sweeps as exempliiled in Figs. 4 and 5 where the average for both figures is +298 volts.

Numerous other arrangementsv within the spirit and scope oi.' the invention will occur to those 'skilled in the art. zdeilned in the following claims.

The scope of the invention is What is claimed is:

1. In a pulse-reflection radar system for marine vessels and coastal defense use, an antenna l,system capable of emitting a pulsed beam of radio energy, said beam being of narrow angular spread in the vertical plane, a scanning mechanism for turning said antenna rapidly backv and forth through an appreciable vertical angle, a lobe switching mechanism for regularly switching the antenna lobe or beam a few degrees in the horizontal plane from a right position to a-left position, a mechanism for coordinating the lobe position and to the left when said antenna beam is in the left position, in synchronism with the emission of exploratory pulses by the radar system and means for actuating said marking element to produce-indications at the precise instante at which reflected energy is received by said antenna system whereby, when a number of reflecting objects are within the area scanned by the antenna beam, there will appear upon the vright and left sides of said indicator screen, patterns of indications the vertical positions of which indicate the vertical angles of the respective'refleeting objects and the horizontal distances of said indications from the vertical center of said screen represent the relative ranges or distances to the respective reilecting objects from the radar system, the right side pattern representing the -reilections received with the antenna lobe in its rightposition, the left. side pattern representing the reflections received with the antenna lobe in its left position and the matching of the amplitude of a right side indicationV with that oi. its corresponding left side indication can be employed to indicate that thev azimuth of that particular reflecting object from which-said indications are received is that of the antenna axis, centrally located between the right and left antenna lobe positions.

2. In a direction and range determining system of the type in which a pulsed beam of exploratory energy is radiated by a highly directive emitting device and reilections thereof are i4 received and timed to determine the range or distance of objects from which reiiected pulses are received, the combination which comprises a iirst means for repeatedly sweeping an arc in a first plane with said emitting device. a second means for abruptly altering the directivity of `said emitting devicel between two positions-approxi- .mately the width of the beam apart in a second plane substantially at right angles to said first plane, the periodicity 'of said `second means being thatot said ilrst means, and a third means for simultaneously presenting, ,in` juxtaposition on a common indicator, two independent patterns oi' indications on separate portions of the screen ci said indicator showing angular direction in saidv ilrst plane versus relative range for each refiecting object, range being indicated for each indication by the distance of the indications from the proximate borders of 'said respective separate portions, direction in saidrst plane being indicated i'or each indication by the transverse position of the indication, one pattern relating to one beam position in said second plane the other relating to the other beam position'in said second plane, direction in said second plane being indicated by the relative intensities of corresponding indications of said two patterns, said third means comprising a cathode ray oscilloscope cooperatively connected with a range sweep generator, a, reversible range sweep amplifier, sources of voltage controlled by said iirst and said second means to control the sweeping action of the ray of said oscilloscope and a radio receiver responsive to echos of said emitted pulsed beam to intensity modulate the ray of said oscilloscope whenever an echo is received, whereby directivity in each of said two planes and the relative ranges of all the objects from which reilections are received can be simultaneously represented.

3. The arrangement defined in claim 2 the said two patterns of indications having a, substantially common boundary along which angular direction in the said ilrst plane is represented and a fourth meanscomprising an adjustable delay unit cooperatively associated with the range sweep generator, for adjusting the effective range scales of both patterns to bring any selected indication in one pattern and its corresponding indication in the other pattern into close proximity with respect to each other near said' common boundary whereby the relative amplitudes of said selected indications can be more readily compared.

4. In an object locating system, means for emitting a highly directive pulsed energy beam, means for receiving reilections of said energy beam andv determining the distance of objects from which reilections are received, means for rapidly sweeping said beam repeatedly through an are in one plane, means for switching the beam repeatedly between two closely adjacent positions in a. second plane at right angles to said rst plane after each sweep of said beam through said arc and means for presenting injuxtaposition on a common indicator two independent patterns of indications on separate portions of the screen of said indicator showing elevation and range of all objects from which reilections are received, one pattern corresponding to reflections received with the beam in one position and the other corresponding to reilections received with the beam in the other of said two closely adjacent positions range being indicated for each indication by the distance of the indication from the proximate borders of said respective separate l5 portions, direction in said iirst plane being indicated for each indication by the transverse position of the indication, direction in said second plane being indicated by the relative intensities of corresponding indications of said two patterns, said last stated means comprising a cathode ray oscilloscope cooperatively connected with a range sweep generator, a reversible range sweep amplifier, sources of voltage controlled by said antenna sweeping and said antenna beam switching means to control the sweeping action of the ray of said oscilloscope and said receiving means being cooperatively connected to intensity modulate the ray of said oscilloscope whenever an echo of said pulsed energy beam is received, whereby information concerning the range and the angular directivity in both said planes of all objects from which reflections are received, is presented simuitaneously.

WILLIAM I-I. DOHERTY.

16 REFERENCES crrnn The ,following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,189,549 Hershberger Feb. 6, 1940 2,405,930 Goldberg Aug. 13, 1946. 2,412,703 Wolff (1) Dec. 17, 1946 2,415,566 Rhea Feb. 11, 1947 2,415,981 Y Wolf! (2) Feb. 18, 1947 2,418,143 Stodoia Apr. 1. 1947 2,419,567 Labin .--i Apr. 29, 1947 FOREIGN PATENTS v Number Country Date 552,072 Great Britain -1.--- Mar. 22, 1943 497,147 Great Britain Dec. 9, 1938 

